1. Field of the Invention
This invention relates to a transducer for detecting pressure changes in pipes to detect changes of internal pressure in, for example, injection pipes of diesel engines or piping of oil pressure equipment, by detecting deformation of steel pipes (hereinafter abbreviated as "transducer").
2. Description of the Prior Art
As a transducer for detecting pressure changes in pipes, there is known a transducer which is a pressure sensor using strain gauges or piezoelectric elements directly mounted on the inner wall of a fuel injection pipe of a diesel engine. To install this transducer in the pipe, a part of the fuel injection pipe must be designed to be opened, and the transducer must be put in or taken out of the pipe through this opening. Therefore, when installing the transducer in the pipe, if the fitting of the opening is imperfect, dust gets into the pipe, possibly clogging the injection pipe. This can result in trouble in the fuel injection system or malfunction of the engine itself.
For avoiding such problem, it is known to a transducer outside the pipe. For example, Japanese Patent Publication No. 58-40133 discloses a transducer in a structure in which a curved piezoelectric element is mounted in tight contact around a pipe, and an elastic holder is disposed between this piezoelectric element and a rigid transducer case which wraps around the outside of the piezoelectric element. Since the piezoelectric element of this transducer is tightly held against the pipe by its holder, if the pipe is deformed, a strong frictional force is created between the pipe and the piezoelectric element, so that the deformation of the pipe is accurately transmitted to the piezoelectric element.
In this transducer, a thin piezoelectric element, for example, is used as a sensor element. Since the sensor element detects changes in the peripheral length of the pipe, not changes in the diameter of the pipe, it is necessary to transmit the pipe deformation accurately to the sensor element. Therefore, in order to transmit the pipe deformation accurately to the sensor element, the pressing force between the pipe and the sensor element must be adjusted.
In this transducer, meanwhile, inertial force acts on the sensor element due to the vibration of pipe caused when the pressure in the pipe rises suddenly, and noise is formed in the output signal of the transducer due to forces other than fluctuation of the pipe internal pressure. To lower this noise, it is required to make the case of the transducer of a rigid structure, to mount the case of the transducer firmly on the pipe, and for the sensor element to be completely free from supporting the sensor element itself. For this purpose, in this transducer, the mounting structure of the sensor element is complicated, and adjustment when mounting becomes difficult. PG,5